The Nervous System Part 2- Electrical Activity in Axons and the Synapse

Question 1

Na+ is more concentrated ________ and K+ is more concentrated ________.

Answer 1

Na+ - Extracellularly
K+- Intracellularly
Play into the potential difference and charges of the cell.

Question 2

Excitability/Irritability refers to what?

Answer 2

A physiology aspect of neurons and muscle cells abilities to produce and conduct changes in membrane potential.

Question 3

When the membrane permeability increases for a specific ion, which results in movement of that ion down its concentration gradient, what kind of an environment is that happening in?

Answer 3

A very small localized environment. It doesn’t mean the whole cell becomes permeable to the ion, just a limited specific patches of the membrane where specific ion channels are located.

Question 4

What does an oscilloscope show?

Answer 4

Shows the voltage between two recording electrodes over time displayed as a line. Measuring the changes in potential difference inside and outside a membrane.

Question 5

Resting Membrane Potential in Neurons?

Answer 5

-70 mV

Question 6

Resting membrane potential in heart muscle cells?

Answer 6

-85 mV

Question 7

Depolarization (Excitatory)

Answer 7

caused by the opening of Na+ channels, called depolarization because if using a oscilloscope the potential difference between the extracellular electrode and intracellular electrode would become less different (inside is becoming more positive)

Question 8

A return to resting membrane potential is known as?

Answer 8

Repolarization

Question 9

What is the period called when the inside of the cell becomes more negative than the resting membrane potential?

Answer 9

Hyperpolarization (Inhibitory)

Question 10

What are the two types of channels for K+

Answer 10

Voltage Gated Channel- The gate is closed at resting membrane potential.
A Channel that is NOT gated- Called “leakage” channel, always open.

Question 11

What are the channels like for Na+?

Answer 11

They are all gated, and the gates are closed at the resting membrane potential. (sometimes they flicker allowing small amounts of Na+ into the cell)

Question 12

What is the threshold in neurons? and at what point does it have to be reached if an action potential is to be generated?

Answer 12

Threshold: -55 mV

Needs to reach threshold by the initial segment of the axon.

Question 13

What happens when threshold is met?

Answer 13

Na+ Channels open, Na+ rushes into the cell. (remember this is happening at a very specific and small region of the cell)
=DEPOLARIZATION
Na+ channels are only open for a fraction of a second, quick ball and chain (a polypeptide chain) closes them quickly.

Question 14

What is +30 mV (sometimes said to be +40 mV)

Answer 14

It is the Peak of the Action Potential.

Question 15

Depolarization is caused by opened Na+ channels. Those channels however close due to an inactivation process, but just before they do the depolarization stimulus causes what?

Answer 15

Causes the gated K+ channels to open. Causes the membrane potential to move toward potassium equilibrium potential (K+ is rushing out of the cell at the localized spot).
=REPOLARIZATION

Question 16

Na+ and K+ channels are both stimulated by depolarization, that makes those ion channels in the axon membrane ____ ____ channels.

Answer 16

Voltage Gated Channels

Question 17

Na+ channels depolarizing leads to the opening of even more Na+ voltage gated channels opening. What feedback is utilized?

Answer 17

Positive Feedback Loop.

Question 18

K+ channels open due to the depolarization of the cell, causing K+ to rush out of the cell, driving the membrane potential back towards the resting membrane potential, repolarization, what feedback is completed here?

Answer 18

Negative Feedback Loop.

Question 19

The changes of Na+/K+ diffusion and the resulting changes in the membrane potential they produce, constitute an event called what?

Answer 19

Action Potential / Nerve Impulse

Question 20

Opening of Voltage Gated K+ channels causes repolarization of the cell. But the K+ causes the membrane potential to slightly overshoot the resting membrane potential, what is this period called?

Answer 20

Hyperpolarization, or after-hyperpolarization. Just dips below resting potential of -70 mV, doesn’t actually reach the membrane permeability for K+ which would be -90 mV.

Question 21

What pump is required to maintain the concentration gradients needed for the diffusion of Na+ and K+ during action potentials? These same pumps are also required to move Na+ out of the axon and to move K+ back into the axon after an action potential to restore resting conditions.

Answer 21

Na+/K+ pump
-If a neuron was poisoned with cyanide it could still produce action potentials for a limited time, because it uses diffusion methods to create an action potential. But without ATP to utilize the Na+/K+ pumps, eventually there wouldn’t be a gradient that allowed for nerve impulses.

Question 22

An increase in frequency is what shows a larger stimuli in action potentials, not an increase in amplitude. Action potentials are therefore said to be an “____ _ ____ ___”

Answer 22

All or Nothing Event.